DISTINCT · StackMonsters

SELECT country FROM customers returns 12 rows: CA three times, US twice. To list each country once, add DISTINCT.

sql

SELECT DISTINCT country
FROM customers;

SELECT country

DISTINCT keeps one row for each different value

DISTINCT goes right after SELECT. It removes duplicate rows: rows that are equal in every column of the result.

Several columns

With more than one column, DISTINCT keeps each different combination:

sql

SELECT DISTINCT country, is_member
FROM customers;

SELECT country, is_member

CA appears twice: (CA, true) and (CA, false) are different rows

DISTINCT works on the result, so it uses only the columns in the SELECT list. You can sort the result with ORDER BY too.